Carrier type transducers are known in the art. These transducers may take the form of resistive bridges or linear voltage differential transformers. These type of transducers are excited by a sinusoidal drive signal. When the transducer is subjected to force or stress, an AC return signal is produced which is proportional to the amount of displacement experienced by the transducer.
For example, a resistive bridge transducer may be placed on a beam in order to measure the beam flexure. The resistor values of the bridge are typically selected so that the output signal from the transducer will be zero volts AC when the beam is in an unloaded condition. Once the beam is flexed, an AC return signal is produced proportional to the amount of the overall flexure.
In order to determine the significance of the transducer return signal, the return signal is measured with respect to the sinusoidal drive signal of the transducer. Unfortunately, several factors will typically cause the transducer return signal to exhibit a phase shift relative to the sinusoidal drive signal when the transducer is subjected to force. Such factors include stray capacitance in the lead lines leading up to the transducer or stray capacitance in the transducer itself.
The return signal from the transducer is typically measured with respect to the sinusoidal drive signal. The return signal can be considered to be a vector which can be plotted on a Cartesian coordinate system. The X-axis represents the sinusoidal drive signal which is known in the art as the phase axis. The Y-axis represents a sinusoidal signal 90.degree. out of phase with respect to the X-axis. The Y-axis is known in the art as a quadrature axis. Since the return signal is out of phase with respect to the sinusoidal drive signal, the return signal vector typically will lie between the phase and the quadrature axis. The measure of the return signal with respect to the sinusoidal drive signal will therefore be only an indication of the X-component of the return signal vector and not the full value of the vector magnitude.
As those skilled in the art will appreciate, varying phase shifts due to the above-mentioned factors will cause inconsistent results for return signals having the same magnitudes. The phase shift also causes inconsistent readings to occur when a different transducer is substituted which exhibits a different phase shift or the length of the lead lines are altered.
An object of the present invention is to provide a new and improved phase compensation circuit wherein the inherent reactance of transducers and associated electrical components, tending to create an output signal phase shifted with respect to a reference signal, are automatically compensated.
Another object of the present invention is to provide an automatic phase compensation circuit that will automatically zero the average return signal to permit measurements of amplitude fluctuations about the average zero value.